The present invention relates to a polymer compound, manufacturing method and use thereof, and sintered bodies manufactured therefrom.
Ceramic Injection Molding (CIM) and extrusion represent two important methods for ceramic molding. In these processes a polymer compound must be initially manufactured by dispersion of ceramic particles in a high-viscosity polymeric matrix. The desired shape is obtained by processing such a mixture by ceramic injection molding or extrusion. After removing the organic auxiliary materials (debindering) a ceramic blank is obtained, which is compressed by sintering. In order for this sintering to result in a dense body, the content of ceramic solids in the blank must be sufficiently high, over 40% by volume, i.e., the polymer compound must also be filled at least 40% in this case.
Powders with particle sizes in the nanometer range are always present in the agglomerated form. The strength of the agglomerates, known as an agglomerate hardness, depends on the previous history of the powder. The spectrum ranges from Van der Waals interaction forces to hydrogen bridge bonds to true sintering necks. In order to reduce the tendency to agglomerate, the powder surfaces are protected with synthetic auxiliary materials. It is, however, considered a disadvantage in this case that no high temperatures can be used in producing the powder, so that the powders often still contain amorphous components. Furthermore, it is also considered disadvantageous that auxiliary materials interfere with subsequent processing.
In manufacturing ceramic blanks by extrusion or CIM and in producing highly filled plastics, normally powders whose specific surface area does not exceed 15 m2/g are currently used. Thus, powders with a relatively low specific surface area are used. This is explained by the fact that finer powders tend to agglomerate to a relatively much higher degree and their agglomerate hardness and the related energy required for breaking up these powder agglomerates is also much higher when such breaking up is even possible.
There are however applications in which a large surface area of the fillers is desirable. Interactions between fillers and the surrounding matrix increase with increasing surface area/volume ratio. The desired properties of particle-filled plastics are defined by these interactions.
Zirconium dioxide powders can be sintered using powder metallurgy to obtain bodies with less than 5% porosity. This material contains tetragonal grains, a mixture of tetragonal, monoclinic, and cubic grains, or only monoclinic grains. The tetragonal phase is stabilized by a small particle size, by doping with foreign elements, high temperature, intrinsic pressure of the material structure, and external pressure. In the following, the small particle size is referred to as particle size stabilization and the intrinsic pressure of the material structure is referred to as structure stabilization. Zirconium dioxide having mixed phase components exhibits intrinsic stresses of the structure, which stabilize the tetragonal component.
These intrinsic stresses result in very high material strength. However, zirconium dioxide having mixed phase components could be previously produced only using more than 1 mol-% of doping materials, which is considered disadvantageous. Known doping materials include Y2O3, CaO, CeO2, or MgO.
The object of the present invention is to provide a polymer compound and a method for manufacturing it in which a dispersion of free nanocrystalline ceramic particles occurs.
This object is surprisingly achieved by a polymer compound containing a ceramic powder and a polymer, the powder having a specific surface area of more than 1.8xc2x7108 m2/m3 and constituting more than 5 vol. % of the polymer compound, the polymer being shear resistant, and the pore sizes in the polymer compound being 3-15 nm.
It is also the object of the present invention to arrive at a zirconium dioxide sintered body having a very high strength by using a polymer compound and no more than 0.8 mol % of doping substances.
This object is achieved by the fact that the ceramic powder in the polymer compound according to the present invention constitutes more than 40 vol. %.
In a particularly advantageous manner, a blank manufactured from this polymer compound according to the present invention can be sintered at temperatures 200-300 K. lower than with the powders used according to the related art.
Preferably the ceramic powder constitutes more than 40 and less than 50 vol. % of the polymer compound.
Furthermore, the polymer compound preferably additionally has one or more saturated or unsaturated C2-C18 carboxylic acids and/or one or more saturated or unsaturated C2-C18 alkyl-dimethyl-substituted chlorosilanes and/or one or more saturated or unsaturated C2-C18 alkylamines.
The ceramic powder in the polymer compound preferably has a specific surface area of more than 2.5xc2x7108 m2/m3.
Furthermore, a polymer compound in which the polymer includes a polyolefin, a polyester, or a polyamide as a thermoplast is preferred.
HD polyethylene, LD polyethylene, copolymers of polyethylene with vinyl acetate or butyl acrylate, polypropylene, or polypropylene grafted with acrylic acid or maleic anhydride are preferred as polyolefins.
Polyethylene copolymerized with vinyl acetate has up to 50% vinyl acetate; polyethylene polymerized with butyl acrylate has up to 30% butyl acrylate. Polyethylene grafted with maleic anhydride has 3% maleic anhydride and polypropylene grafted with acrylic acid has 6% acrylic acid.
Polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polylactone are preferred as polyesters. Polyamide 6, polyamide 12, and polyamide 66 are preferred as polyamides.
Oxides such as ZrO2, Al2O3, SiO2, MgO, TiO2, Y2O3, carbides, nitrides, or their mixtures are used as preferred ceramic powders. All kinds of zirconium dioxides, including those containing other metal oxides, are suitable as ceramic powders for the polymer compound. Furthermore, alpha, gamma, and delta aluminum oxides, as well as all simple and complex oxides having a basic or amphoteric surface are suitable, ceramic powders, and particularly preferred is amorphous SiO2 (Aerosil(copyright)). When using silicon dioxide, the use of a silane dispergator is particularly preferred. Among carbides, silicon and tungsten carbides are particularly suitable. Si3N4 and AlN are particularly well-suited as nitrides, an amine being preferably used as a dispergator.
The simple and very quick compounding of the powder into the mixture in a single piece of equipment, the kneader, is particularly advantageous in the method according to the present invention. Another advantage is the possibility of obtaining a heterogeneous material system whose properties are only determined by the interactions of the components at the phase boundary surfaces.
Thermoplasts having a strong tendency to thermomechanical degradation accompanied by predominant or full decomposition are not suitable for use in the method according to the present invention.
Another object of the present invention is a method for manufacturing the polymer compound using a ceramic powder and a thermoplast, the ceramic powder having a specific surface area of more than 1.8xc2x7108 m2/m3 and the thermoplast being a shear-resistant polymer kneaded in a kneader with such a high shear force that the pore sizes in the polymer compound are 3-15 nm when the polymer is filled with at least 5 vol. % ceramic powder.
Using the method according to the present invention, even agglomerated powders can surprisingly be disintegrated down to their primary particle sizes, whereby polymer compounds and bodies manufactured thereof with the above-mentioned pore sizes can be manufactured.
In the method according to the present invention, a mixture of an agglomerated ceramic powder having a primary particle size of xe2x89xa630 nm and an agglomerated particle size of 1 xcexcm or more, a dispergator such as a carboxylic acid and a thermoplast highly resistant to shear forces is processed in a kneader with such high shear forces that the powder is disagglomerated and its primary particles are thereby disintegrated and protected by the dispergator. The dispergator protects the primary particles from re-agglomeration.
Using the method according to the present invention, solid contents of up to 57 vol. % are achieved in the polymer compound. Furthermore, pore sizes of down to 3 nm with a narrow distribution are achieved using the method. These two findings clearly show that the agglomerate has been broken up. Agglomerated powders are normally unsuitable for ceramic process technology and cannot be disagglomerated to this degree using grinding processes of any type.
Using the shearing process applied in the method according to the present invention, the specific surface area of the powder remains the same or is increased. This could be verified using nitrogen adsorption at 77 K by the BET method.
The pore sizes in the blank were measured using N2 desorption or Hg porosimetry. Here it was found that the average pore sizes are smaller by a factor of at least two than the average powder pore sizes measured in the same manner. Furthermore, it was found that they have a narrow monomodal distribution of the pore volume over the pore diameter.
Adding saturated or unsaturated carboxylic acid(s) during compounding as a dispergator results in a chemical reaction of the carboxylic group with the powder surface. In this reaction the carboxylic group is converted into the resonance-stabilized, negatively charged carboxylate group, which is deposited on the positive charge centers of the powder surface, so that an adsorptive ionic bond is obtained. This could be verified via Fourier transform IR spectra for decanoic acid as a dispergator and zirconium dioxide.
In using saturated or unsaturated alkyl dimethyl substituted chlorosilanes as a dispergator, a reaction takes place between the powder surface and the chlorosilanes. The use of dimethyl alkyl chlorosilane as a dispergator for nm-range carbide powder has been found particularly advantageous, the alkyl radical including the C1-C18, radical.
The pore sizes in the polymer compound with appropriate filing of the organic component are between 3 and 15 nm. Thus the mobility of the macromolecules is strongly reduced up to a tested temperature of 300xc2x0 C. This results, in a particularly advantageous manner, in a thermomechanical behavior where the storage modulus of the polymer compound according to the present invention remains virtually constant up to a temperature of 300xc2x0 C.
The polymer compound manufactured by the method according to the present invention can be used as a starting material for ceramic molding by injection, extrusion, warm or cold pressing, calendering, or rolling. Dense ceramic blanks and, after debindering and sintering, dense ceramic bodies and bodies with definite open and/or closed porosities can be manufactured.
The polymer compounds according to the present invention can be present as molded bodies in the form of string or hollow string of any desired cross-section, a tube, a rectangle, or a sheet. Thus, for example, strings with a diameter of 6 mm to 8 mm, 14 mmxc3x973 mm tubes, 4 mmxc3x975 mm rectangles, and 10 mmxc3x971 mm sheets, in particular, 75 mmxc3x970.5 mm sheets have been manufactured.
Polymer compounds in the form of injection molded bodies or complex three-dimensional bodies can be manufactured.
The polymer compounds according to the present invention are also well-suited as a particle-reinforced plastic.
In addition, the polymer compounds according to the present invention are well-suited as a master batch for manufacturing filled plastics. In particular, functional fillers, for example, for coloring, with dielectric properties (insulators), electrical conductivity, and/or UV adsorption, are used.
Sheets manufactured by the method according to the present invention were found to have the particular advantage of flexibility, which is necessary for printability. In this case normal thick-layer technology is used. When used for printing, it has been found that good compatibility exists with organic systems of the printing pastes, in particular with polyvinyl butyral and high-boiling ether- and ester-based solvents.
The polymer compounds according to the present invention are also well-suited for use as printed circuit board materials.
Previously used printed circuit board materials include aramide fiber-reinforced plastic or fiberglass-reinforced epoxy resins. These materials are, however, not fully satisfactory.
A printed circuit board material having matching thermal expansion coefficients to minimize thermal stresses in integrated components and their electrical contacts was sought. Furthermore, a dielectric material for connection and dielectric planes subsequently applied on FR4 printed circuit board carriers, such as RCC foils (resin-coated copper foils), which equalize the expansion coefficients between the core material and components, is sought. Furthermore, a dielectric material for mounting semi-conductor components on metallic heat sinks with improved heat conductivity and adapted thermal expansion coefficients is sought.
Printed circuit boards manufactured from the polymer compounds according to the present invention achieve these objects through improved thermal conductivity compared to known printed circuit boards, reduction of the thermal stresses as a result of reduced thermal expansion coefficients and, when nanocrystalline amorphous SiO2, is used, also as a particularly readily available and inexpensive embodiment. Thermal expansion coefficients of 0.5 ppm/K and a thermal conductivity of 1.3 W/mK can be achieved.
Reinforcement with nanocrystalline particles can increase the continuous use temperature of simple thermoplasts to approximately 200xc2x0 C. Even when the polymer contains more than 5 vol. % fillers, the thermal expansion coefficients are lower than those of conventional printed circuit board materials and a good match with the thermal expansion coefficients of chips is achieved. The optimum for this application of the polymer compounds is at a filler content of 40-50 vol. %.
The thermal expansion coefficient of the mixture is greatly reduced by 5-8 ppm/K compared to pure polymer. The stresses occurring due to thermal cycling in mounted components and their contacts are thus minimized.
Furthermore, thermal conductivity is increased compared to pure polymer and compared to printed circuit board materials of the related art.
By using Aerosil(copyright), the continuous use temperature is increased to over 200xc2x0 C. compared to a pure polymer. Thus the substrate is also resistant to lead-free solder having a higher fusion point, for example.
The polymer compounds according to the present invention are also well-suited as casting compounds for electric or electronic components.
Another advantage of the method according to the present invention and use of the products manufactured using this method is that none of the materials used constitutes a hazard to the environment and each can be used in industrial process without any problems due to their high or nonexistent maximum allowable concentration thresholds.
Examples of Manufacturing of the Polymer Compound